Water Rocket Forum

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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Guess I could have answered my own question by reading the entire statement...

Rocket can be any shape or size but cannot exceed 1,500 grams. This is the total dry weight of all flying components in a flight ready condition including the pressure vessel, fins, nosecone, payload bay, camera, altimeter, flight computer, deployment system, batteries, and nozzle.(no reaction mass) A heavy mass falling from high altitude can be very harmful to persons or property.

The source of my confusion came from reading NAR, FAA, NFPA rules and trying to understand how they reconcile with WRA. Did this drive y'all nuts?

NAR:
Size. My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.

FAA:
(a) Class 1—Model Rocket means an amateur rocket that:
(1) Uses no more than 125 grams (4.4 ounces) of propellant; (ok that's specific)
(2) Uses a slow-burning propellant; (does this remove water rockets from Class 1 definition?)
(3) Is made of paper, wood, or breakable plastic; (does this mean they don't want us to use flexible plastic?)
(4) Contains no substantial metal parts; and (wow could they have used a more vague term?)
(5) Weighs no more than 1,500 grams (53 ounces), including the propellant. (I'm reading this as total liftoff weight)

NFPA:
Water powered, why would they care about water rockets? If we assume that the word propellant (which isn't defined by itself in the NFPA code) means a substance that produces thrust through combustion, water rockets have none. They define model rockets as having "model rocket motors" and model rocket motors must have "solid fuel propellant". Oh and mass launches now have to have expanded safety perimeters? Boy, every world record attempt for multiple launches sure violates that! They also want to discourage people from making "home built" rocket motors. Good thing water rockets don't have motors!